To meet the power specifications of different electronic products, various electronic devices, such as power adapters, power transformers and power connectors have been provided in the art. In such electronic devices, a housing is used as a covering to isolate interior electronic elements from dust or mist or from being contacted by a user.
Referring to FIGS. 1 to 4, an existing housing includes a first housing part 1 and a second housing part 2 coupled with the first housing part 1. The first housing part 1 includes a first joint portion 11, a first outer surface 12 and a first inner surface 13. The first outer and inner surfaces 12, 13 extend from the first joint portion 11. The first joint portion 11 is stepped and has a first projecting portion 112 adjoining the first inner surface 13, and a first shoulder portion 111 indented from the first projecting portion 112 and proximal to the first outer surface 12. The first projecting portion 112 has a plurality of linearly aligned and spaced-apart ribs 113 protruding therefrom. The ribs 113 are equidistantly spaced apart from each other and form a welding line (L1) continuously extending parallel with the outer surface 12. The second housing part 2 includes a second joint portion 21, a second outer surface 22 and a second inner surface 23. The second outer and inner surfaces 22, 23 extend from the second joint portion 21. The second joint portion 21 has a second projecting portion 211, a second shoulder portion 212 and an inner projecting portion 213. The second projecting portion 211 adjoins the second outer surface 22. The inner projecting portion 213 adjoins the second inner surface 23. The second shoulder portion 212 is indented between the second and inner projecting portions 211, 213. The first and second joint portions 11, 21 are interlockable with each other.
When the first and second housing halves 1, 2 are coupled with each other, the first shoulder portion 111 is in contact with the second projecting portion 211, and the ribs 113 are in contact with the second shoulder 212. By ultrasonic welding, the ribs 113 are formed into a bonding layer between the first projecting portion 112 and the second shoulder portion 212, thereby bonding the first joint portion 11 to the second joint portion 21.
Each rib 113 is a triangular prism, and is tapered away from a surface of the first projecting portion 112. In order to increase the coupling strength of the first and second housing halves 1, 2 so as to pass the drop and falling ball tests, the ribs 113 have to be melted as efficient as possible during ultrasonic welding to increase the adhesion strength of the first and second housing halves 1, 2. However, when the ribs 113 are melted, because each rib 113 is relatively large in width or cross section, especially near a seam between the first and second housing parts 1, 2, each rib 113 produces a relatively large amount of melt. The melt is liable to overflow through the seam due to vigorous vibration caused by ultrasonic wave, thereby adversely affecting the aesthetic appearance and yield rate of production.
When the amount of the melt is reduced to avoid the problem of melt overflow, adhesion between the first and second housing halves 1, 2 is insufficient. During the drop and falling ball tests, because the welding line (L1) is continuous, even a small break in the welded joint can cause the welded joint to split entirely, thereby resulting in test failure.